The invention relates to an electrode formed of low conductivity material. Typically such electrodes take the form of an elongate hollow body. Preferably the body is made of a substoichiometric oxide of titanium or the like in which case it is likely that the most effective manufacturing route will result in the body being porous.
It has been calculated, by way of illustration, based on a tubular body 500 mm long, 18 mm outside diameter with a 3 mm wall thickness, made of a material with a volume resistivity of 30 mΩ.cm, operating with an electrical connection at the one end, supplied with a current of 2.83 Amps (intended to provide a current density of 100 A/m2 at all points along its length) that there will be a voltage drop of about 750 mV between the ends of such an electrode. In many electrochemical applications and as a result of this voltage drop there may be regions of the electrode where the potential is insufficient to perform its intended function. In the case of an electrolytic process operating at low voltages of the order of 1 to 5V between anode and cathode (the preferred situation since this leads generally to lower electrical costs) it cannot be guaranteed that all the surface area of the electrode will be equally effective, or effective at all. This is particularly true of electrolytic processes, such as water treatment, which are favoured by electrode surfaces which exhibit high gassing overpotential (such as titanium suboxides, lead dioxide, doped tin dioxide etc). In such cases, the actual current density can be shown to vary by more than 50% between the ends of such an electrode.
It is one object of this invention to provide a method of making an electrical connection to such an electrode which will solve this problem, particularly in the context of the electrode body being made of a porous material.